In large electrical machines it is common to use a so called double-layer winding. This winding type has the benefit that all coils are identical and the coils are easy to manufacture.
However, in electrical machines with a high number of poles and a small pole pitch the traditional double layer windings can be difficult to mount because an insertion of a last coil within dedicated slots require to lift a first coil out of the slots while completing the winding of the coil.
Furthermore, for a segmented electrical machine double layer windings require coils that connect across the segment joint.
It is possible to make single-layer windings that do not require the removal of the first inserted coils when inserting the last coils in a stator. It is also possible to make single-layer windings that do not need to cross segment joints. Consequently, single-layer windings can be advantageous for large electrical machines.
Single-layer windings normally require both in-plane and out-of-plane end windings. The manufacturing of the in-plane end windings is straightforward, but the manufacturing of the out-of-plane end windings is more difficult. This normally comprises the steps of first forming a plane coil and then deforming to the desired out-of-plane shape. This final deformation is intensive in work and may introduce small defects in the insulation due to the relatively large elongations of the material.
The EP 1 852 958 A2 discloses a method for an automated forming of single-layer coils. This method eliminates the majority of drawbacks by traditional forming but it requires a fairly elaborate machine arrangement with a coil winding tool, which rotates around two axes. So this is a complex machine, controlled by complex algorithms.